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Fluke 87 III True rms measures wrong currents

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Paul1977

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- In the 10Adc range I measure 166mAdc instead of 1Adc.
- In the 400mAdc range I measure 54mAdc instead of 400mAdc.
Has anyone an idea which component is broken and where I can find it?

Thank you for reply and best regards, Paul
 

KlausST

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Hi,

please be sure to use the right connections. There are different connections for A and mA.

****

If connections are right.
Where do you know that you really have 1ADC or 400mA DC?

the relation is not equal: 1.00A / 0.166A = 6; 400mA / 54mA = 7.4
(Therfore i don´t expect the voltage reference to be broken)

If the shunt burnt, then i there should be higher readings than expected. This isn´t the case.
Maybe there is a fuse in series to the power path....

The meter doesn´t show an overflow, so i expect the ADC to be OK.

Therefore i expect the failure somewhere between power path and ADC. Maybe there is an RMS_to_DC circuit.... Check the input and output voltages .


Good luck
Klaus
 

Paul1977

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I have used the right connections for A and mA.
Also the battery is ok.

Indeed the relation between A and mA is not equal.

There is only a relation when measuring in the same range, see in more detail below what I have measured.
I use a lab power supply and two multimeters in series (one good multimeter and the meter with wrong current measurement)

Ampere range"
Good multimeter wrong multimeter
1000mA 164mA
2000mA 326mA
3000mA 488mA
4000mA 650mA
5000mA 810mA
6000mA 970mA

milliAmpere range"
Good multimeter wrong multimeter
100mA 13mA
200mA 26mA
300mA 39mA
400mA 52mA

Thank you for help.
 

Anna Conda

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You (or someone) has killed this meter pretty good on the amp measure ranges, this is usually done when some one leaves the leads plugged into the AMPS sockets and then goes to measure the mains volts - BANG - if the fuse has been replaced with a non HRC quick acting type, it lets thru enough energy to damage the circuitry... this is most likely what has happened and no one has fessed up to the incident....
 

Paul1977

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Fluke is fixed!

The diode after the bridge rectifier was shorted.
Diode is replaced and everything works great.
Thanks for help.

Best regards, Paul
 

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